Capacitive touch sensing is increasingly used in musical controllers, particularly those based on multi-touch screen interfaces. However, in contrast to the venerable piano-style keyboard, touch screen controllers lack the tactile feedback many performers find crucial.
The TouchKeys (described, for example, in A. McPherson. TouchKeys: capacitive multi-touch sensing on a physical keyboard. Proc. New Interfaces for Musical Expression, Ann Arbor, Mich., USA, 2012) are a set of hardware sensors which attach to the surface of an existing keyboard, and which use capacitive touch sensing to measure the position and contact area of the fingers on the key surfaces (up to 3 touches per key, in 2 dimensions). Further relevant work is the development of a keyboard measuring continuous key angle rather than the more typical note onsets and releases (McPherson and Kim, “Augmenting the acoustic piano with electromagnetic string actuation and continuous key position sensing”, Proceedings of the 2010 Conference on New Interfaces for Musical Expression).
Other relevant prior art includes the Moog Multiply-Touch-Sensitive keyboard from 1990, which used a capacitive sensing arrangement to measure finger position, the Endeavour Evo touch-sensing keyboard (2012; endeavour.de), the Roli Seaboard musical controller (2012; weareroli.com), and the Haken Continuum controller (2007; hakenaudio.com).